Various methods of straightening hair are known, each having it's own advantages and disadvantages to a more or lesser degree. Hair straightening technologies include those that alter the primary protein structure of hair, those that alter secondary or tertiary protein structure, and those that hold hair in a straightened configuration against the hair's natural tendency to curl.
In parent application U.S. Ser. No. 13/013,482 (herein incorporated by reference, in its entirety), we disclosed new and useful hair straightening compositions comprising polylysine and transglutaminase, preferably also sodium metabisulfite, Na2S2O5, and optionally tourmaline and calcium; in a cosmetically acceptable base maintained at a pH of 5.0 to 7.5. The efficacy of the composition was dependent on the pH. However, although such products are effective hair strengtheners, over time we have noticed that efficacy diminished. In the present invention, our solution to this problem results in new and improved hair straightening compositions.
Human Hair
U.S. Pat. No. 5,395,490 is herein incorporated by reference, in its entirety. Several figures in U.S. Pat. No. 5,395,490 diagram the structure of human hair fibers, the protein components of hair, and energy levels of the disulfide bond. A fiber of human hair comprises three main morphological components: the cuticle, the cortex, and the cell membrane complex, which itself is comprised of a protein matrix of keratin peptide chains.
The natural shape and structural integrity of human hair depends, in part, on the orientation of disulfide bonds (cysteine-cysteine bonds). In human hair, disulfide bonds that link one part of a peptide chain with another part of the same chain contribute to tertiary protein structure, while disulfide bonds that link two different peptide chains contribute to quaternary structure. Furthermore, disulfide bonds are known to protect secondary protein structures in the immediate vicinity of the bond. They may do this by shielding hydrogen bonds.
Thus, it is generally thought that alteration of the disulfide bonds is necessary and/or useful to effect long term changes in the shape of hair. Hair shaping treatments that do not rearrange the disulfide bonds result in changes in hair shape that last a relatively short time. For example, the use of heat to style hair may create temporary straightening of the hair. However, the styled hair will return to its natural shape after a short time, as a result of exposure to moisture in the air or washing. The use of heat and moisture to straighten hair may break and reconfigure hydrogen bonds in the hair, but the disulfide bonds are not substantially affected. It is thought that hydrogen bonds, by themselves, are insufficient to hold the shape of hair for a significant time, because the stronger disulfide bonds eventually force the hair to reassume its original shape. Thus, a permanent straightening of the hair is thought to involve the cleaving and reforming of a substantial number of disulfide bonds. Various chemical treatments for doing this are known.
Chemical Hair Straightening Treatments
Hair straightening by treating the hair with chemical agents is well known. Depending on the straightening agent used, damage to the protein structure may be controlled to a more or less degree. That is, various types of protein structures of the treated hair may be broken down, or only a select type of protein structure. For example, hair straightening products that alter primary structure, do so by weakening and/or breaking the internal chemical bonds of hair protein amino acids. Regardless of where the protein structure is altered, effective straightening treatments cause natural curls to loosen and straighten. While some straightening agents may be more effective and/or efficient than others, the trade off is usually in the damage done to the hair and scalp, and the need for adjunct treatments to limit that damage. On the other hand, treatments which may be somewhat less damaging to the hair and scalp, may require a longer time to operate, or the application of significantly more product, or multiple applications to achieve a desired result.
Among known hair straightening products that alter primary structure we may name products comprising sodium hydroxide, potassium hydroxide, lithium hydroxide, and guanidine hydroxide. It is generally acknowledged that repeated use of hydroxide hair straightening products can be very damaging to hair.
Among hair straightening products that disrupt tertiary, and perhaps quaternary structure, we can name ammonium thioglycolate, ammonium sulfite, ammonium bisulfite, sodium metabisulfite (Na2S2O5), and cysteine. These sulfur-containing agents are more targeted in the damage that they inflict on hair proteins. These agents act primarily by selectively weakening or cleaving the disulfide bonds in cystine, instead of disrupting the entire protein. First, the sulfur-containing agent is used to reduce disulfide bonds, along with the application of mechanical stress. Next, new disulfide bonds are allowed to form, in a new arrangement, thus giving the hair a new shape. An oxidizing agent may be used to help constitute the new disulfide bonds. In the art of hair straightening, repeated use of ammonium thioglycolate or cysteine is considered significantly damaging to hair, while ammonium sulfite and ammonium bisulfite also cause damage.
Hair straightening products based on formaldehyde are also known, and have come under some scrutiny by health authorities in recent months. In general, known chemical treatments are considered harsh and damaging to human hair and skin. The damage done to hair is measured as a loss of cystine content (fewer S—S bonds indicating a loss of protein structure), a decrease in water contact angle (loss of hydrophobicity), an increase in microscopic damage to cuticle (swelling and lifting), a decrease in mechanical break strength. Some visible manifestations of the negative effects of chemical hair styling include dry, brittle or limp hair, and a loss of shine and/or color.
In addition to the damage that various salon and retail hair treatments may cause to hair, the risk posed to a user's health is also a concern. Any health risks that may exist pertain to the person whose hair is being treated, but more especially they pertain to hair styling professionals who experience repeated or persistent exposure to hair treatment chemicals and/or to chemicals that are generated in the process of treating the hair. In general, a retail consumer or a salon professional may come into physical contact with hair treatment chemicals and/or be exposed to vapors given off by hair treatment products. Skin irritation, allergic reaction and headaches are some of the symptoms of excessive exposure to one or more chemicals that may be found in commercially available and professionally available products. A product that does not elicit an adverse reaction, even after extended exposure, is certainly preferred over less benign products.
Transglutaminase
Transglutaminases are a family of enzymes with the ability to covalently bond protein bound glutamine and protein bound lysine. Transglutaminases (hereinafter, TGase) catalyze the posttranslational modification of proteins by transamidation of available glutamine residues. A major result of this activity is glutamyl-lysine cross-links in proteins. Glutamine is readily available in hair, while lysine is present to lesser degree. Some TGases are found naturally throughout the body, including the hair. Other TGases are present in animal, plant and microbial sources. Available sources of transglutaminase include, but are not limited to, slime mold, alfalfa, guinea pig, and bacteria. Used topically, TGase may contribute to the overall protein structure of hair.
Commonly owned, co-pending application, US2009-0126754, discloses the use of topically applied transglutaminase (without any free lysine) to retain curl in curled hair. However, it was also reported that when a commercially available transglutaminase blend was present at concentrations of 2%, 5% and 10%, the product caused curled hair to droop, within 30 minutes of application, by as much 25%, 33% and 16% respectively. Despite this, curl was not eliminated completely, and the hair was not straightened to a sufficient degree to consider these products as commercially viable hair straightening products, based on TGase alone.
A number of other topical uses for transglutaminases have been proposed. JP 2719166 discloses compositions containing transglutaminase and a polyhydric alcohol, said to be useful in treatment of damaged hair by increasing the moisture retention of the hair. JP 3-083908 suggests the use of transglutaminase in combination with polyethylene glycol or other water soluble materials to treat chapped skin. It has also been suggested for use in binding active components to skin, hair or nails (U.S. Pat. No. 5,490,980). WO01/21145 teaches the use of transglutaminase to improve the color-fastness of hair dyes. WO01/21139 suggests a combination of transglutaminase and an active substance having substrate activity for transglutaminase, for use in restructuring damaged keratin fibers. U.S. Pat. No. 5,525,336 discloses the combination of corneocyte proteins and transglutaminase for application to skin, hair or nails to form a protective layer.
Tourmaline
Hair straightening products that alter secondary or tertiary structure include those that comprise tourmaline. Tourmaline is an acentric rhombohedral borosilicate characterized by six-membered tetrahedral rings. It is a semi-precious stone, and a crystal silicate compounded with varying amount of elements such as aluminum, iron, magnesium, sodium, lithium, or potassium. The beneficial effects and advantages of heat activated tourmaline on hair proteins has been discussed at length in commonly owned applications WO2010/096598, WO2010/096605, and WO2010/096610, herein incorporated by reference, in their entirety.